Jodhpur is fondly known as the "Sun City" as the sun seems to rise here first every morning. It was Rao Jodha who first discovered the city and so it was named after him. Like you said, the Mehrangarh Fort is quite a famous tourist attraction here. But here's a list of some of the other best attractions in Jodhpur:

The Jaswant Thada. This is a cenotaph dedicated to Maharaja Jaswant Singh II. It was made using delicate marble materials with intricate carvings. You can find portraits and paintings of different Rathore Rulers inside the Jaswant Thada. You can find this 1 km Northeast of the Mehrangarh Fort.

The Umaid Bhawan Palace. Considered to be one of the last palaces to be built in India, you can still find the royal family of Jodhpur residing in one area of the palace. You'd have to stay in the palace though to be able to explore it and unfortunately, it's kind of a steep price. If you have the money though, why not? There's a museum though which costs Rs. 50 to enter for non-hotel guests.

The Balsamand Lake. It was Balak Rao Parihar who initiated the construction of this artificial lake. You can find various groves of fruits here like papaya, mango and even guava.

The Kailana Lake. This was constructed by Pratap Singh. You can ride a boat to enjoy the entire lake. Or you can just view it from the side and enjoy the birds flocking nearby. Make sure you time your visit in the sunset as it can be quite an amazing scenery to watch from here.

Rao Jodha Desert Rock Park. You can explore this 70 hectares of land with various plants from the Thar Desert. Entry fee costs Rs. 30 for adults and Rs. 10 for kids.

The Old City Markets and The Clock Tower. The Clock Tower was built by Maharaja Sardar Singh and offers a great view of the fort. Alongside of it are various markets selling different knick-knacks.

Mandore Gardens. There's also a museum here for an entry feee of Rs. 50. Otherwise, just explore the park along with the different cenotaphs, temples and statues found here.